This invention relates to an arrangement for the measurement of phase noise of a test specimen according to the preamble of the independent claim.
In phase noise measurement of signals of a test specimen using a spectrum analyzer, phase noise of mixing oscillators of the spectrum analyzer is added to phase noise of the test specimen. Test specimens, therefore, can only be correctly measured if their signal-to-noise ratios are at least 5 dB worse than for the spectrum analyzer (Ulrich Rohde, "Microwave and Wireless Synthesizers," Chapter 2.8.2).
To avoid this disadvantage, it is known to construct two identical test specimens and to mix these in a mixer at 0 Hz (Ulrich Rohde, Chapter 2.8.5). Using this process, the actual carrier of the test specimen disappears and then only noise sidebands are measured, the phase noise of the spectrum analyzer itself not being included. A disadvantage of this known process is that two identical test specimens must be present.
To suppress a carrier it is also known to use specialized so-called notch filters, which however must be of high quality.
It is an object of this invention to provide a structurally uncomplicated arrangement with which phase noise can be measured with a spectrum analyzer even of test specimens which, compared with noise characteristics of the spectrum analyzer, have relatively good noise characteristics.